Bridges provide a passageway for people, vehicles and/or materials. There are many different types and designs of bridges, including beam bridges, arch bridges and suspension bridges. From a historical perspective, the moveable bridge is one of the more recent developments in the design of bridges. Moveable bridges, also known as drawbridges, number approximately 2800 throughout the United States. Drawbridges are unique from other types of bridges in that the moveable span(s) or module(s) of the draw bridge is comprised an open grid deck structure. This framework of open grid bars is composed of steel and provides a stable load-bearing structure. It offers the advantages of being relatively light weight (i.e., minimal dead load) compared to solid concrete/steel structures and has low impedence or resistance to the flow of air or wind currents when the drawbridge is in the opened position. The open grid structure also offers a free-draining surface for water drainage during wet seasons. Open grid deck systems have found other applications in other types of load-bearing structures across the country, including bridge overpasses and railroad crossings, numbering over 3200 and 280,000 respectively in the United States.
This open grid deck structure, however, presents a significant safety concern for motorists. In times of wet weather during rain or snow, the steel framework surface of the open grid deck structure becomes very slippery and promotes fish-tailing and skidding of motor vehicles. As a consequence, hundreds of automobile accidents occur, yearly, on open grid systems throughout the United States. Many of these accidents involve fatalities. Undoubtedly, society would be greatly benefitted by safer bridges with open grid deck structures that provide a greater degree of traction for motor vehicle tires during periods of wet weather or other adverse conditions, such as gasoline and oil spills.